Mesososo, Was this a past issue even before the installation of Windows 7?
If so, this issue could be caused due to the fact your graphics driver does not fit the needs to play the game in full screen. This issue could be resolved by upgrading your graphics driver in your pc.
If games worked fine before the installation of Windows 7, Then you could be missing drivers and I would recommend you to locate drivers for your specific graphics card and download/install them.
I've had this issue before running Windows XP, which was due to the fact my graphics card did not fit the needs to play the online game. I had to upgrade the graphics card which did cost money ($$$) but is worth it if you would like to play the games in full screen.